US2128233A - Electron tube - Google Patents

Description

Aug. 30, 1938 w. DALLENBACH ELECTRON TUBE 2 Sheets-Sheet 1 Filed March 1,. 1935 In veniar:

WALTER DZF/VBACH ATTOFF/VE/S Aug. 30, 1938. v w. DALLENBACH ELECTRON TUBE Filed March 1, 1955 2 Sheets-Sheet 2 //7 vemop:

ATTOFi/VEYS Patented Aug. 30, 1938 ELECTRON TUBE Walter Diillenbach, Berlin-Charlottenburg, Germany, assignor to N. V. Machinerieen-en Ap- 'fiaten Fabrieken- Meaf, Utrecht, Nether- Application March 1, 1935, Serial No. 8,938

Germany March 1, 1934 9 Claims. (Cl. 250-275) The present invention relates to an electron tube for the purpose of exciting, i. e. generating, amplifying or receiving high-frequency electromagnetic oscillations, particularly oscillations of a wavelength of less than m.

The essential component parts of ultra-short wave tubes of this description are the exciting electrode system, the' frequency determining resonator connected therewith and the aerial 10 coupled with the frequency determining resonator. -With a suitably selected connection, e. g.

feed-back connection, brake-field connection or magnetron connection it is possible to reduce the damping of the resonator in consequence of the influence of the stream of electrons passing over between the electron system or to cause the resonator to be excited for producing oscillations.

As resonators the invention contemplates employing not only oscillating circuits with separated self-induction and capacity, but also such circuits, in which the self-induction and the capacity have been distributed over the conductors more or less uniformly. In the former case the resonators of the known ultra-short wave tubes are made to consist of a single wire circle as selfinductlon and the electrodes as capacity. In the secondcase parallel conductors, so-called Lecher wires are used for forming a resonator which, at a potential loop, are provided with the electrodes required for excitation. For this oscillatory effeet to be attained with a resonator of such nature, the value is decisive, in connection with which L represents the self induction, C the capacity and R the total clamping resistance over which the oscillating circuit is made to flow. In a resonator in which capacity and self-induction have been uniformly distributed over the conductors, se1f-, induction and capacity forL and C have to be inserted per cm. The value will also be referred to as wave resistance or surge impedance (W), so that instead of also W2 R- 5 may be written.

In the known resonators employed in ultrashort wave-tubes, the value in OR or of is essentially smaller than that of resonance circuits employed in high frequency technics. The cause thereof is to be found in the fact, that in the ultra-short wave resonators constructed so far, the values of C and R, in relation to the'very small self-induction L, could not be made small. Particularly the value R, being composed of the Ohms resistance, the leak resistance and the radiation resistance, above all, owing to the growing radiation losses of the resonator in conjunction with increasing frequency,'will be very large. In consequence of 'these great losses at the resonator, the potential amplitudes atthe electrodes of the tube necessary for the control of the electron stream, remain small, when compared to the D. C. potentials connected up, so that the tube will work with a low degree of efliciency only.

The object of the. present in'vention is an electron tube for the purpose of exciting electro-magnetic oscillations with the aid of a resonator, in which the drawbacks, detailed above, have been obviated. In accordance with the present invention a resonator is employed, consisting of a hollow space, limited all-round, by means of metallic, well conducting walls, the natural damping of which can be kept exceedingly small. With the aid of such a resonator construction the radiation damping, which has most to be considered, has practically been reduced to zero. Also the Ohms damping of the resonator can be kept within very small limits, if the surfaces, limiting the hollow space, are made to consist of a well conducting metal, for instance, silver or copper, whichhas been provided with a, high polish. In consequence of the special, constructive measures detailed in the examples of performance, leakage losses have also, practically speaking, been avoid-' A further characteristic feature of the present W resonator and loading resistance is required.

resistance may be connected with the resonator. It has been ascertained, that in connection with the most favorable adaptation of the loading resistance to the resonator, the value W2 'E must be comparable with a value S representing the relation of the alternating current, obtained through the medium of the control in accordance with the order of magnitude, coincides with the value For this reason, a very loose coupling between This loose coupling can be attained with the aid of an energy line or conductor with a low surge impedance. An energy line or conductor, consisting of two co-axial leads, which is not subject to radiation losses, is advantageously employed. If an energy line or conductor is employed, the

length of which approximately coincides with.

the quarter wave length or an odd multiple of the oscillation to be excited and if the energy line or conductor is connected with the resonator in the potential node, a potential at the free end with no load will present itself which, in relation to the surge impedances of the energy line or conductor and the resonator is lower, than the maximum alternating potential amplitude in the resonator. A loading resistance, connected with the free end of the energy line or con ductor, will then represent to the resonator a damping resistance, which is smaller than the loading resistance, and that relatively to the squares of the surge impedances of the energy line or conductor. It has, thus, been rendered possible, by making the slit-shaped space, representing the energy line or conductor, suf iciently narrow, thereby forming an appropriately low surge impedance, to couple the loading resistance, particularly the aerial, as loosely with the hollow space, as may be required.

Further characteristic features of the present invention result from the constructive connection of the electrodes, necessary for the excitation, with the metal walls limiting the hollow space resonator. In view of the fact, that for exciting a resonator at least two electrodes are required, which must be kept under diiferent D. C. potentlals, the hollow body, consisting of metallic conductive walls limiting the resonator space, is so constructed as to consist of at least two parts insulated from each other. At a suitable point the metal walls will then be designed as electrodes. For the purpose of avoiding at the joints possible leakage or loss radiation, various ideas of solving the problem have been indicated, which are elucidated in the examples of performance. Further characteristic features of the present invention may be gathered from the description and from the patent claims. Examples of performance of the present invention have been represented in .the Figs. 1-41).

The Figs. 1 and 2 show graphically and in section hollow space resonators limited by two metallic bodies insulated from each other and provided with'short circuit condensers for the purpose of avoiding leakage'or loss radiation. The

structure is enclosed within a vacuum tube.

surge impedance, has been represented in Fig. 1,

as enclosed within a vacuum tube represented diagrammatically by the reference character '1,

although this may be avoided by employing an arrangement such as will be described later in connection with Fig. 3. The resonator consists of the cylinder condenser I and the single turn toroid coil 2, situated therein, as self-induction, being subdivided by the cylinder condenser 3 serving, as short circuit for-the ultra-high frequency.

The two cylinders of the condenser l are to serve as electrodes. In view of the fact, that the clearance between the electrodes has to be selected generally in due consideration of the electron mechanism and does not permit of being made so narrow as in the condenser 3, it is advisable to assemble two elements in accordance'with Fig. l to form an arrangement according to Fig. 2, for the purpose of avoiding the leakage or loss radiation presenting itself at the open end of the elec trodes. The electrode capacity, attained by the cylinder condenser I, will then join symmetrically on each side asingle turn coil 2 and '2' which, in consideration of the D. C. potential be tween the electrodes, are each divided by means 1 of a condenser 3 and 3. In arrangements of this nature it will be possible, in contra-distinction to'a concentric Lecher system, to limit the capacity of the oscillating circuit to a minimum, i. e. the minimum demanded by the electrode surface. The two shells of the toroid act, under practical working conditions, like an inductance, the magnetic flow of which is made to pass as a circular flow through the cross section represented in Figs. 1 and 2. The leakage or loss radiation at the free ends of the condensers 3 and 3' may be neglected. Relatively to the concentric Lecher system the arrangement embodies the advantage, thatit may be of shorter length in an axial direction. In a Lecher system the length s, see Fig. l or 2, would have to be selected so as to correspond to of the wavelength, whilst in arrangements according to Figs. 1 and 2 the length s may be considerably shorter than A of the wavelength.

The inner lead is formed as an electrode serve ing as acylindrical condenser l and i respectively in Figs. 1 and 2, and as the grid 28 and 28 in order to be able to start the oscillation of the resonator. A cathode 29 and 29 respectively is provided at the axis of the grid and serves to produce the glow electron emission.

Fig. 3 represents an electron tube fitted with a hollow space resonator corresponding to Fig. 2.

In the center of the rotary-symmetrical arrangement a cathode l, in form of a hair-pin like filament has been provided between the two bolts 5 and 5'. The hot cathode and-the bolts are concentrically surrounded by a metal tube 8 which, at its middle part, is provided with a grid' 1 consisting of bars running in a direction parallel to the axis. The metal tube 6 is, in turn, surrounded by a rotary-symmetrical metal body. the part 8 of which is made to serve as electrode and part of the condenser and the parts 9 of which are made to serve as a single turn coil and part of the inductance ofthe resonator. The tube-shaped part III, joining the lower end of the resonator forms, together with the tube 8, a short circuit condenser, while the tube-shaped part II, joining the upper end forms, together with the tube 6, an energy line or conductor of low surge impedance. The length-of the energy line or'conductor is suitably made to equal one quarter of the wavelength. The upper end 01' the inner conductor 6 is made to terminate in the quarter wavelength aerial I2 and the-upper end of the outer conductor H in the plate l3 for the capacitative transmission of the aerial current.

In order to avoid in the tube the employment of a special vacuum vessel, the upper end of the energy line or conductor has been closed up by means of a glass fusing I4, so as to render it vacuum tight. while to the outer conductor of the short circuit condenser at the lower end a glass sleeve l5 has been fused, through which the current leads l6 are made to pass into the interior of the tube. The glass sleeve is further advantageously adapted to carry the branch I! for connecting the tube to a vacuum pump. The outer meiallic jacket of the tube is thus made to essentially serve as vacuum vessel.

In order to keep down the escape of leakage or loss rad ation to the lowest possible extent, the space between the two tubes 6 and I0. which are forming the short circuit condenser at the lower end, should be made as small as possible. The space between the tubes 6 and H forming the energy. line or conductor. should be made to be so large, that through the medium of its surge impedance the most favorable adaptation of the aerial I 2 to the resonator will be attained. This most favorable selection of the surge impedance of the energy line or conductor is best determined with the aid of experiments. I

The hollow resonator space intended for excitation is limited by the metallic cylinder 6, the grid 1 and the outer metallic jacket, consisting of the parts 8 and 9. The potential loop of the oscillation is formed between the grid 1 and the tube part 8. ,The ultra-high frequency alternating field passes partly through the gaps of the grid 1 to the interior of the cylinder 6 and to the cathode. In order to avoid there a disturbing excitation of resonance spaces and a leakage of oscillatory energy via V the current leads, the interior space of the cylinder 6 has been provided with the two bolts 5 and Simounted so as to be insulated, the outside diameter of the bolts being only little smaller than the interior diameter of'the tube 8. They thus form with the tube 6 short circuit condensers and limit within the grid 9. space, the

natural frequency of which is higher than that of the resonator to be excited. The space between cathode and grid cannot thus be excited either in its first harmonic or in any one harmonic.

For the purpose of reducing the damping of the resonator or for the excitation of oscillations of same, different connections may be made use of. The brake field connection will be employed advantageously, in connection with which the grid ismade to acquire a highly positive and the anode or brake electrode 8 a potential in the proximity of zero or a negative potential. The electrons, passing from the cathode, partly hit' the bars of the grid, while another part thereof penetrates into the space between grid and anode. In an oscillating tube the ratio of the stream of electrons striking the bars of the grid to the stream of electrons passing through the grid and de scribing a turning movement in front 01' the anode in order to return to the grid, is changed. Therefore, owing to the oscillation between grid and anode, a control of the stream of electrons, penetrating into the grid anode space, takes place at the grid proper. The electron alternating current produced thereby, always yields with the alternating field existing between the grid and the anode a power delivery,'if the duration of transmission of the electrons from the grid to the reversing face in front of the anode equals about of the duration of period of the ultra-high frequency oscillation. v

The electrons passing through the grid 1 in the direction towards the anode, are subjected to a braking effect not only on their way there, but also on their return path by means of the high frequency field, thus transmitting energy, imparted to them by the constant field existing between 4 and I, to the resonator. nating potential, up to which the resonator rises, is sufliciently powerful, the electrons will be subjected already during their reciprocal motion to a braking effect of such strength, that they strike the grid I on their return from the anode 8 approximately at the speed zero. Under these conditions an optimal utilization of the constant field energy transmitted to the electrons will 'take place.

If the alterthese electrodes together with the conductor parts forming the oscillating system, eg the two con,- ductors of a Lecher system, form a system open in itself, permitting stray radiation, but that this system, open in itself, is enclosed in a closed metallic hollow body closed all around preventing stray radiation.

Figs. 4, 4a and 4b represent an examplebf performance ofv a magnetron tube of this description in longitudinal section and in two cross sections la-la and lb-db. The reference numeral 4 represents the cathode, preferably in the form of a so-called hair-pin cathode. The electrodes I 0,.

l8 are so-called slit anodes and form the two conductors of a Lecher system of the half wavepreventing the escape of stray radiation, and thus reducing the damping connected therewith. At one end thebolts 20, 20' of semi-circular cross section are made to serve as condensers, which 4- amazes not only among themselves, but also with the tube l9, are made to form narrow, slit shaped interstices. The slit between 20, 20 is simultaneously made to serve as energy line or conductor. The emitter 2| has been coupled at the outer end of the bolts 20, 20'.

The left end of the resonator has been closed by the plates 22, 23, 24, forming the short circuit condenser in order to prevent the escape of leakage or loss radiation. The plates are insulated from each other and provided at the edge with a glass fusing 25. In the same way the right end of the energy line or conductor has been provided with a glass fusing 26, so that the tube may be evacuated without being equipped with a special vacuum vessel. The coil 21 has been provided for the purpose of producing an axial magnetic field.

Reference is made to my c'o-pending applications Serial No. 20,089 and Serial No. 747,948.

,What I claim, is:

1. A vacuum discharge tube comprising two coaxial, axio-symmetrical metallic hollow members forming an outer conductor and an inner conductor, said members being spaced for part of their extent to form a resonator, the outer and inner conductors being spaced apart at another part of their extent to form a concentric high frequency conductor of slight wave resistance, part of said outer conductor having a substantially continuously unbroken surface sealing said resonator against radiation losses and constituting a solid wall electrode, said inner conductor being provided with openings'adjacent said resonator and serving partly as a grid, and a coaxial cathode within said grid.

2. A vacuum discharge tube comprising a wire cathode, a cylindrical grid co-axial about said cathode, a cylindrical solid wall electrode co-axial about the grid, other wall portions connected to both ends of the grid and solid wall electrode, each of said other wall portions forming a single winding torus coil, the grid, the solid wall electrode, the saidother wall portions, and torus coil comprising a resonator, short circuit condensers on the torus coils connected with the electrodes, one of said short circuit condensers comprising a high frequency conductor.

3. A vacuum discharge tube comprising a wire cathode, a cylindrical 'grid co-axial about said cathode, a cylindrical solid wall electrode coaxial about said grid, other wall portions connected to both ends of the grid and solid wall electrode, each of said other wall portions forming a single winding torus coil, the grid, the solid wall electrode; the said other wall portions and the two torus coils comprising a resonator, a short circuit condenser secured to one of said torus coils connected to the electrodes, cylindrical high frequency conductors of the length M4 of slight wave resistance connected to the electrodes by the other torus coil, said conductors being comprised of inner and outer leads, the inner lead continuing as an aerial of M4, a metal plate perpendicular to the aerial and connected to the end of the outer lead of the high frequency conductor.

4. A vacuum discharge tube comprising a cathode, a cylindrical grid co-axial about said cathode, a cylindrical solid wall electrode coaxial about the grid, co-axial wall portions connected to'the grid and to the solid wall electrode, said wall portions each forming a torus coil, said solid wall electrode and said coil forming an electromagnetic resonator of slight natural damping, a' co-axial and cylindrical conductor connected to each-of said torus coils, said conductors forming a high frequency line of slight wave resistance.

5. A vacuum discharge tube comprising, a cathode, a cylindrical grid co-axial about said cathode, a cylindrical solid wall electrode coaxial about said grid, co-axial wall portions connected to the grid and to the solid wall electrode and forming torus coils, said solid wall electrode and said coils forming an electromagnetic resonator of slight natural damping, co-axial and cylindrical conductors. having the length )\/4'con nected with said toms coils, said conductors forming high frequency lines of slight wave resistance.

6. An electron tube comprising two hollow cylindrical conductors, one of said conductors being insulatingly spaced from and within the other conductor to form an inner conductor, portions of said conductors being uniformly closely spaced from each other to form a condenser, and other portions being relatively vfurther spaced from each other to form inductances, a cathode within said inner conductor, an area of said inner conductor a'djacent'said cathode forming an electrode, whereby an oscillating circuit may be maintained in said tube.

7. An electron tube as in claim 6, second similarly closely spaced portions forming a second condenser, said second condenser including a slit-shaped space through which high frequency energy can pass, and an energy lead connected to said second condenser.

. 8. A tube as in claim 6, said area consisting of a layer of material of good electrical conductivity.

9. A tube as in claim 6, said area consisting of a layer of material of good electrical conductivity and being polished to increase the electrical conductivity thereof. g

- WALTER DALLENBACH.

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